The majority of selective calling paging receivers available on the market include multiple independent addressing capability. This means that more than one signalling code can be used to cause the alerting mechanism of the paging receiver to activate. The receiver decoder when built in at the factory, must be capable of recognizing several independent addresses and thus causing an alert actuation.
In many applications for selective calling paging receivers, it is highly desirable that the paging device be able to receive and decode more than one address signal. It is especially important in some applications, such as public safety, to be able to alert a group of individuals with one paging signal while retaining the ability to alert or signal individual members of the larger group. This requirement for multiple independent addresses is by no means universal however, and providing this capability presently adds a considerable cost to the paging devices, and penalizes the single address or non-group call users.
In normal commercial usage, the vast majority of such paging receivers are used simply to notify the user to call a specified number such as his office. Thus, for the normal user of paging services, the decoder and therefore the receiver that he uses, is generally far more technically sophisticated than he would normally require. Much of the original cost of the selective call paging receiver lies in the design and the construction of the multiple independent address decoder mechanism. A less complicated decoder combined with the capability to add on a multiple address feature if required could result in a lower cost paging receiver.
The present invention is intended to lower the cost of the basic decoder for digital codes while allowing for virtually unlimited multiple independent address decoding capability by means of add on or replacement modules. The modules are customarily referred to as code plugs. This invention provides a way for adding the ability to decode multiple independent addresses to a basic single address digital paging decoder, and thus solves the cost problems associated with the previous multiple independent address design approaches. This invention also allows the decoding capability of a pager to be upgraded by means of replacement of the code memory or code plug, and does not burden the basic decoder device with the cost of all of the circuit elements required for multiple independent address decoding. Thus, the cost of multiple address decoding is only born by the users who need it. This approach places the cost burden for utilization for multiple address capability decoding on the users who need such capability.